Method and apparatus for coating the interior wall of hollow bodies



March '7, 1933., A. M. HAGEMAN ET AL METHODAND APPARATUS FOR-COATING THEINTERIOR WALL 0F HOLLOW BODIES Filed Dec. 9, 1927 3 Sheets-Sheet lINVENTOR AJVI. HAGEMAN A. F. L/ND e0 ATTORNEY March 7, 1933. A, M.HAGEMAN ET AL METHOD AND APPARATUS FOR COATING THE INTERIOR WALL OFHOLLOW BODIES Filed Dec. 9, 1927 3 Sheets-Sheet 2 INVENTOR A.M.HHGEMANA. M. HAGEMAN ET AL March 7, 1933.

METHOD AND APPARATUS FOR COATING THE INTERIOKWALL OF ROLL 0W BODIES asheets-sheet :5

Filed Dec. 9, 1927 INVENTOR A. M HAGEMAN ,4. F. Lnvos-r M BY Q ATTORNEYPatented Mar. 7, 1933 UNITED STATES PATENT OFFICE AARON H. HAGEHAN, OIBLOOMIIIILILD, AND ALBERT I. LINDSTROM, OF N UTLEY, NEW JERSEY,ASBIGNOBS 'I'O WBTINGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIAMETHOD AND APPARATUS FOR COATING THE INTERIOR WALL OF HOLLOW BODIESApplication filed December 9, 1927. Serial No. 238,734.

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In the manufacture of incandescent electric lamps, it is important to beable to provide a bulb, which is made either of a light diffusinvitreous material or of a clear glass bul having a coating of a lightdiffusing character and at the same time, obtain a maximum lightefliciency. It has been proposed to obtain light difiusing effects bythe employment of a so-called opalescent or opal glass. The opa lescenteffect being attained by addin cryolite to a batch of glass during manuacture. This was an exp'enslve procedure and furthermore, such glassacts to decompose liberating gases, probably silicon-fluoride which aredetrimental to the filament and shorten the life of the lamp.Furthermore, the light absorption .by reason of opal glass is extremelyhigh and inasmuch as it is-not possible to.

obtain a uniform thickness of a bulb, the resultant transmitted lightvaried in intensity.

The nearest approach to the opalescent ef feet in connection with coatedlamps was attained by the application of a coatmg to the outer surfaceof the bulb such, for example, as that set forth in Patent 1,613,758January 11, 1927. I

The outside coating of bulbs, however, although giving a satisfactorylight diffusing medium, did not attain the desired opalescent effectwhich may be defined as a light difl'using medium enclosed in a glossyor highly polished surface as the exterior surface of a lamp bulb. Ithas been proposed to etch the inside surface of a lamp bulb with an acidsuch as a hydrofluoric acid or other etching solution. This methodphysically changes the inner surface of the bulb, breaking the same intonumerous minute hills and valleys which reflectlight at all angles andcause a diffusion of-the emitted light. Theetched surface, however, didnot answer the requirement of producing a desirable opalescent ef fect,since the intensity of .a lamp filament is too great to be diffuseduniformly by the roughened surface of the bulb and although thetransmitted light was diffused to an appre ciable degree, a concentratedspot of light alwaysremained visible. Furthermore, the etching of a bulbby means of acid required the exercise of extreme care, since the acidfumes were deleterious to the workers and extreme caution was necessaryin performing the etching operation.

The present invention aims to provide a lamp bulb with a light diffusingcoating so arranged that the coating in combination with the smoothexterior surface of the bulb gives the desired opalescent or pearlyeffect.

As set forth in our copending application Serial No. 737,609 filedSeptember 13, 1924 for coated article and method of making the same, thedesired opalescent effect is attained by app-lying a light diffusingmaterial to the inside "surface of a lamp bulb and it is an object ofthe present invention to provide a method and apparatus whereby suchmaterialmaybe applied in a convenient and expeditious manner.

Another object of the invention is to provide amethod of coating theinside surface of a hollow transparent body with a uniform lightdiffusing layer.

Another object of the invention is toproduce a lam'p'bulb comprising auniform light diffusing layer on the inside surface of a translucentbody which layer in combination with the glossy exterior surface of thebody, will constitute a light diffusing medium, giving the desiredopalescent effect.

The smooth outersurface of a lamp bulb or other container provided witha light diflam may have the required depth of color as w en usingvarious colored pigments.

- The invention is, of course, applicable for the coatin of variousforms of hollow translucent bo ies, but is herein shown and described inconnection with the coating of the inner wall of a transparent vitreousincandescent electric lamp bulb. 1

The above mentioned type of hollow body, namely a lamp bulb, comprises asphere-like portion terminating in a relatively narrow opening or neck.The application of a coating material to the inner surface of this formof hollow body is extremely diflicult, particularly since, it isessential to apply the coating in such manner as to have the same ofuniform density throughout. In an electric lamp bulb wherein a hightemperatured filamentis disposed in close relation to the that anyvariation or defect in the character of the coating will be exa geratedand readily noticeable, giving the ulb an unfinished or defectiveappearance.

In accordance with the present method, therefore, it has been found thatby first heating a bulb to a given temperature then applying a finelydivided material to the inner surface of the bulb, preferably while thebulb is rotating, a layer of light diffusing material may be uniformlydeposited. It has further been found that the coating is best appliedwhen discharged in the form of a. spray such as a coniferous dischargefrom a spray gun nozzle. The discharge is produced within the bulb anddirected to a wall thereof, while a relative movement between the bulband the spray nozzle is effected until the entire surface of the bulbreceives a light diffusing 4'0 layer.

The manipulation of the spray gun is important by reason of the closeworking relation necessary, inasmuch as the spray nozzle is confined tothe space within the bulb. The '45 spray nozzle is introduced into thebulb at an angle to the longitudinal axis of the bulb, after which adischarge of sprayed material is produced. The nozzle is then movedlengthwise of the bulb to direct sprayed ma- 5 terial against thesurface of the bulb from a point adjacent to the neck thereof to a pointat the top of the bulb or the inter-section between the longitudinalaxis of the bulb and the wall thereof. A rotation or relative movementof the bulb and spray nozzle during the spraying operation, preferably arotation of the bulb, results in the deposit of a layer of sprayedmaterial, but as the nozzle moves toward the end of the bulb, the

contour of the bulb is such that the distance between the spray nozzleand the bulb decreases, thus a rotation of the bulb causes the surfaceof the bulb at the narrow portion (or dead center of rotation) near theend to rotate at a less speed than the wider portion.

light diffusing wall, it will be appreciated Normally, therefore, theend of the bulb would receive an excessive amount of sprayed material.To avoid this, the s ray is kept from impinging directly upon t e end ofthe bulb and the spray gun is so manipulated that the body portion ofthe spray coats the inner surface -of the bulb up to a point adjacent tothe end of the bulb and the roving particles of spray which surround themain body of the discharge are sufficient to cover the upper portion ofthe bulb with a layer of the same degree of intensity as is depositedupon the other portions of the bulb in the, direct path of movement ofthe spray discharge.

After the bulb has been sprayed, it is moved into a baking oven todehydrate the coating. This baking operation depends, of course, uponthe character of coating employed.

The present method of coating by the apparatus employedresults in auniform deposit of coating upon the inner wall of a bulb and gives anarticle having a uniform light diffusing medium which, in combinationwith the lustrous outer surface of the bulb provides the desiredopalescent effect.

The invention willbe more fully understood by reference. to theaccompanying drawings in which: I

Fig. 1 is a more or less diagrammatic plan view of an apparatus forpracticing the present method;

Fig. 2 is a side elevational view of the apparatus shown in Fig. l butwith the spray mechanism removed for the sake of clarity;

Fig. 3 is an enlarged plan view of a portion of the machine shown inFig. l and more clearly illustrates the spray gun mechanlsm;

Fig. 4 shows a bulb in position to be sprayed and with the spray gunabout to enter the bulb;

Fig. 5 is av view similar to Fig. 3 which shows the spray gun within thebulb with a discharge of spray projected to the surface of the bulb.

Fig. 6 shows a spray gun in its advanced position within the bulb tospray the upper portion thereof; and,

Fig. 7 is a view showing the spray nozzle in position adjacent to asteam jet for cleaning the nozzle.

An apparatus for practicing the present method may comprise a conveyor10 provided with an odd number of bulb holders 13. In the presentillustration, 37 bulb holders are employed and the conveyor movesintermittently in stages so that every other bulb holder is applied tospraying mechanism. An oven 14 extends about the path of movement of theconveyor so as to receive the mov- The use of the'single oven to preheatthe bulbs and bake the coated bulbs isv accom plished by having theconve or with an odd this bulb will not be removed from the conveyor butwill pass through the oven for a ba ing operation. This is accomplishedby having-means associated with the conveyor atA which operates to ejecta bulb, by means to be in the form of a fan or cone is effected in thelater described, from a holder so that the bulb will drop into a chute17. The mechanism for actuating the holder to, release the bulb opotherholder so that a sprayed lamp will only be ejected upon its secondapplication to the said mechanism which causes its ejection from theholder.

With this arrangement, it will be evident that as the conveyor moves inthe direction of the arrow X a coated lamp and an empty holder will bemoved toward the oven 14. Before the empty holder enters the oven 14,however, the operator at B inserts a new bulb into the holder. Since theconveyor indexes for every two bulbs, the bulb which has already beensprayed will pass the spraying mechanism upon the second revolution ofthe sprayed bulb with the conveyor, this is due to the odd number ofbulb holders in the conveyor. The spraying operation is performed by thespray gun 16, which operation will be hereinafter more fully described.

During the spraying, it is preferable to rotate the bulbs. For thispurpose, each bulb holder may have a shaft 18 supported in bearings 19on the conveyor 10. These shafts may be disposed radially with respectto the axis of rotation of the conveyor and the end of each shaft may beprovided with a pinion 20 positioned to mesh with a gear wheel 21. Thisgear wheel may be mounted on a shaft 22 and driven by means of a'pulley23 connectedwith a suitable source of power (not shown).

As the conveyor moves the bulb holders to the spraying position, thepinions 20 will en age with the gear wheel 21, causing a rotatlon of thebulb. As the conveyor moves each bulb holder away from the sprayingposition, the pinion 20 will be moved away from the gear wheel, thusterminating the rotation of the bulb holder, although it is evident thatif desirable, a series of gear wheels 21 may be provided so that thebulbs may be rotated throughout their movement through the oven.

The foregoing description sets forth the general operation intransporting and positioning the bulbs for the spraying operation. Asmore clearly shown in Fig. 3, the spray mechanism 16 for spraying thebulb comprises a slide plate 24 upon which is mounted a cross-head 25for carrying a spray nozzle erates, however, to remove a bulb from every7 type attac ed toatubular portion throughwhich thefinely divided spraymaterial is caused to flow. The spray materi'al may enter the tubularportion 27 through a flexible tube 28,v which tube, may be connected toa,

container 29- containing the spray'material'.

The container is usually elevated above the 26. The. s ray nozzle maybe; of M21; suitable spray un so that the spray. material nor-- mallyowsby gravity into thespray gun.

The discharge of the spray substantially.

usual manner by the discharge'of air which enters a conduit 30 and isdirected across a tip 31 of the nozzle 26 by means of an angularlydirected outlet orifice 32 as show-nin Figs. 5 and '6. This discharge ofair passin across the nozzle tip 31 results in the usua ejector effectto atomize and project. finely divided material flowing through thetubular passage 27. Means are provided forterminating the flow ofcoating materialexcept when the nozzle 26 is within the bulb. Such meansmay comprise a cam 33 which engages a valve 34 to cut off the air flowwhen the spray gun is in its outer or removed position with respect to abulb. The cam 33. is actuated upon a movement of the spray gun into thebulb by reason of a lever arm 35 extending from the'cam which engageswith a pin 36 on a stationary arm 37. Means for moving the nozzle 26 ofthespray gun into and out from a bulb 15 may comprise a lever arm 38which may be rocked in the direction of the arrow Y by any suitablemeans (not shown). The said arm 38 is provided with a link 39 pivoted at40 to the cross-head 25. An oscillation of the arm 38, therefore, Wlllcause a movement of the said head with a consequent movement of thespray nozzle 26.

In order to properly coat a bulb, it is desirable to move the nozzleintothe bulb at an angle to the longitudinal axis of the latter. This isaccomplished in the present structure by providing the head 25 with aguide finger 41 movable between angularly disposed tracks 42 and 43.These tracks are arranged to lie beneath the bulb when the same is heldin position for spraying. It will thus .be evident that as thecross-head is moved toward the bulb, the nozzle 26 will be guidedtherein. It will be understood that in order to permit a movement of thenozzle and its associated parts in an angular direcat the ends of leversl6 and 4:7. The levers are pivoted on a head 48 slidable'on a shaft 49extending from a hub 50 which is secured to the conveyor 10. At one, endof the shaft 49 is a jaw 51 and a spring 52 disposed between the jaw andthe head 48 serves to normally close the jaws 45 and 46 to grip a bulb.

When the conveyor is in position to eject a bulb, an extension 53 on thehead 48 engages a suitably positioned cam-member 54 causing the head tomove toward the bulb and release the same. The above described mechanismfor holding and discharging abulb is used for preheating the bulb andfor baking the same after the coating has been applied so that thebaking temperature and the preheating temperature are the same,preferably about 350 C. It will be understood, however, that ifdesirable, two ovens may be employed and that the preheating temperaturemay be about 350 C. or above and the baking temperature may be about 350C. or above.

Although any suitable coating composition may be employed, it has beenfound that the present method gives satisfactory results when a coatingis provided containing sodium silicate, a filler such as Kaolin and apigment with a suitable amount of water mixed in a ball mill until ahomogeneous mixture is obtained. A mixture of this character is wellknown in the lamp coating art and is more fully set forth' in Patent1,581,-

In practicing the present method,'bulbs or blanks are fed to the holdersuntil the first bulb is intermittently moved to a position in operativerelation to the spraying mechanism 16. At the spraying station, thenozzle 26 is moved into and out from the bulb to deposit a layer ofspray material on the interior surface of the bulb, which operation ismore clearly shown in Figs. 4 to 6. As will be noted, the nozzle 26travels through a path at an angle to the longitudinal axis of the bulb.It is obvious, however, that the nozzle 26 may be moved througha'predetermined path and the bulb may be held at an angle, in whichcase, the spray nozzle 26 might, for example, be moved horizontally. Theresult of this operation would, however, be the same as moving thenozzle as above set forth.

The spraying of the interior surface of a hollow body such as a lampbulb is a difficult and exacting operation. With the present apparatusthe nozzle 26 is moved into the neck 55 untiladjacent to a point asindicated by the dotted line 56 at which time the spray gun is operatedto vproject a fan or conical shaped discharge 57 of finely dividedmaterial. .Thus the spray is produced within the article. The spray gunnozzle is then moved along the path indicated by the dotted line 58which path has been chosen so as to keep the concentrated portion 59 ofthe spray as far from the surface wall 60 receiving the spray as ispossible. The distance of the nozzle withrelation to the said wall islimited by the dimensions of the bulb.

The importance of heating the bulb prior to spraying will be appreciatedfor the reason that the s ray must not run when it is applied to theulb, but must be in such condition as to readily adhere to the surfaceand cover the same. When coating the outside surface of a bulb, thedistance between the bulb and the spray nozzle may be relatively long,thus the particles may becomparatively dry before reaching the bulb. Thecombination of the sprayed material applied within and to a wallof aheated bulb is an important step in the present method.

As the gun moves into the bulb, thebulb is rotated at relatively highspeed, thus causing an impingement or deposit of the spray material overthe interior surface of the bulb.

Inasmuch as the bulb is rotated about its axis indicated by the dottedline 61, theupper end or tip 62 015 the bulb will be in the dead centerof rotation and rotate at relatively low speed as compared with theadjacent wall of the bulb.

As the spra Y gun moves into the bulb, the' enlarged portlon of the bulbwill receive a certain amount of spray material owin to the length oftime to which the wall oi the bulb is subjected to the discharge ofspray. It has been found that in order to obtain a uniform layer ofsprayed material upon the inside surface of the bulb, the comparativelydense portion 63 which may be termed the main body thereof, should bemoved so that this main body of spray does not reach the top portion 62of the bulb. The spray gun is, therefore, moved until the main body ofthe spray is discharged adjacent to a point on the'dead center ofrotation of the bulb so that the free or roving particles of spray whichare projected from the main body will be deposited upon the upper wallof the bulb to produce a layer which, by reason of the relatively longtime period the upper wall is exposed to the roving particles of spraywill produce a layer of material upon the upper wall equal in densityand thickness to the deposit upon the adjacent wall or the remainder ofthe interior surface of the bulb.

In producing a sprayed lamp bulb, the thickness of the coating may bedetermined by the character of the material used or by the number ofreciprocable movements or 1 into and out from 5 coating 1s desired. thespray nozzle .may be coatin involves the coating and in operationnecessitates bulb neck until the same becomes plastic. If

passes of the spra nozzle, within the bulb.

If a light coating is to be obtained, it may only be necessary toimovethe spray nozzle the bulb, or if a heavier moved back and forthseveraltimes within thebulb. v It will be noted that the present methodof As illustrated in the drawings, the nozzle is shown as' movableimtoandout from the bulb in suchmannerthat the. spray nozzle is held asfarfrom the surface to be sprayed as practical. In practicing the presentmethod,

it .hasalso been found that good'results are obtained by moving thenozzle into the bulb through apath inaccordance with'the contour of thesurface to be coated. By this manner of manipulating the nozzle, theoutlet or discharge orifice of. the nozzle may be maintained a uniformdistance from the bulb.

As hereinbefore mentioned, it has been found that the degree ofthe'density of the coating may be controlled by the number of movementsor passes of the nozzle into and out from the bulb and that the rate of.speed of rotation of the bulb may be varied so that the surface to becoated will be exposed to the spray for a longer or shorter period.

It has further been found that when utilizing the preheating step it ispossible to dispense with the final baking step. The bulb when preheatedacts to dehydrate the applied by leaving out the final baking step theoperation of coating is expedited and a greater quantity of bulbs may becoated in a given time period than has heretofore been possible;

By producing the spray after the nozzle 7 has entered the bulb, it ispossible to avoid a deposit of sprayed material upon the neck of thebulb. This is an advantage since after the bulb has been sprayed it isnecessary to perform what is termed a sealing-in operation. Thisoperation consists in fusing the neck of the bulb to another lamp parttermed a mount which latter part includes the filament and supportingstructure. The sealingthe heating of. the

a deposit of another material such as a coating is applied to the bulbneck, the operation of heating is more difficult, since the coatingabsorbs heat and, therefore, makes it so difficult to properly melt theglass and fuse the bulb neck to the lamp mount.

When employing the present apparatus to discharge a coating materialcontaining sosilicate, a nozzle is employed which disicharges thesprayed material at an angle to bodily manipulation of, 10 a disc arge.of spray within the body to be if a unf form layer is to be applied. Ithas been found, however, that the fine articles of the sprayedmaterialbecome lo ged; be--.

tween the air outlet orifice 32 of the spray nozzle and the tip 31thereof and that these particles build up to such a degree as to offeran obstruction and change theyangle at which the spray is projected. Itwill be evident that if during operation, the angle of the spray ischanged, the accuracy of operation is affected since a greater orlesser-amount of spray will-be deposited upon the upper surface of thebulb. The character of the sodium silicate coating composition issuchth'at the buildingsup of material upon the spray nozzle offers aconsiderable detriment to continuous and effective results. 1

The present invention, however,-"provides meansformaintaining the nozzlefree from an accumulation of material which means consists in the use ofa nozzle associated with a source of steam supply'to project a. jet ofsteam 65 against the nozzle tip. A steam nozzle may be positionedso asto direct discharged steam against the spray nozzle tip to clean thesameafter each movement of the pozzle from a bulb after a sprayingopera- 1on.

By this method, the spray nozzle enters the bulb for each operation insuch condition as to leave it free to operate for the discharge of thespray at the predetermined angle. It i has been found that, With thepresent com-' position of coating using sodium silicate, that themoisture of the steam combined with its heat and the velocity with whichit is" pro ected from anozzle, serves to cut the 1 sodium silicate andkeep the nozzle clean. It is, of course, obvious that any other fluidmaybe employed as moist hot air or fluid of such characteras to serve toremove the particular composition used for the coating.

Inasmuch as the jet of fluid is projected against the nozzle. after eachoperation of,

the same-for acoating of a bulb, air projected at high velocity willserve to. remove any particles of composition should they'adhere toofirmly to the nozzle. The use of steam, however, not only dislodges theparticles and by reason of the moisture afiects a more complete removalof any material that may be come deposited upon the nozzle tip orbetween the tip and the air outlet orifice.

The present method and apparatus not only serves to coat the interiorsurface of bulbs in an efiective and eflicient manner to produce alayerof uniform density and thickness, but by'reason ofthe present meth-0d, the lamp bulbs may be coated at the high rate of speed required inconnection with other lamp making operations, whereby coated lampsmay beproduced at a minimum cost.

is shown, it

Although apreferred embodiment ofapparatus for practicing the presentmethod isto be understood that modifi-. cations may be made therein aswell as variations in the method without departing from the spirit andscope of the invention as set forth in the appended claims.

What is claimed is: I

1. An a paratus for depositing a layer of a light di usin material uponthe inner surface of a lamp laulb which comprises mechanismhaving a.spray discharge orifice 'for light difl'using material, means for movinsaid mechanism into and out from said bulb and means for preventing anaccumulation of spray material adjacent to said orifice.

n apparatus for depositing a coating of light diffusing material uponthe inner wall of a lamp bulb which comprises a spray nozzle having aconduit for spray material and an outlet orifice for directmg a spray ofmaadjacent to one side of terial at an angle to the longitudinal axis ofsaid conduit, means for moving said nozzle into and out from said bulband means for preventing accumulation of sprayed material adjacent tosaid outlet to maintain the I discharge material at the required angle.3. An apparatus for spraying a light difside of said bulb, means forcausing a spray discharge against the opposite side of said means forrotating said bulb about its lon ltudinal axis, means for heating thebulb so t at the coating materialwill pass through a heated environmentand become partially dry before deposit upon said bulb and willcompletely dry upon striking the heatedbulb to ve a smooth uniformnon-flowing layer.

l ii testimony whereof, we have hereunto subscribed our names this 8thday of December, 1927. J

AARON M.'HAGEMAN." ALBERT F. LINDSTROM.

fusing material on the interlor surface of a transparent hollow body oflight transmitting material having a constricted neck por-- tion and anenlarged body portion, comprising a spray gun having an extensionforconucting spray, material, a nozzle at the free end of said extension,means for moving said extension to cause said nozzle to travel into saidbody through a path intersecting the longitudinal axis of said body,means for causing a discharge of spray material at a predetermined pointin the path of travel of said nozzle and means for rotating said bodyabout said axis.

4. An apparatus for spraying a light diffusing material on the interiorsurface of a transparent hollow bo y of light transmitting materialhaving a constricted mouth portion and an enlarged body portion,comprising a spray gun having an extension for conductin coatmgmaterlal,a nozzle at'the free end 01 said extension, means for moving saidextension to cause said nozzle to travel through a path so as to disposethe nozzle said body, means for actuating said gun to cause a dischargeof sprayed material against the opposite side of said body and means forrotating said body about its longitudinal axis during-the discharge ofsprayed material, An apparatus for coating the interior surface of alamp bulb having a constricted neck with a light difi'using material,comprising means for heating the bulb, a spray nozzle having asprayoutlet orifice, means for moving said nozzle into said bulbthrougha path intersecting the longitudinal axis of deposit of ightdiffusing

